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Asilidae
The Asilidae are the robber fly family, also called assassin flies. They are powerfully built, bristly flies with a short, stout proboscis enclosing the sharp, sucking hypopharynx.12 The name "robber flies" reflects their notoriously aggressive predatory habits; they feed mainly or exclusively on other insects and as a rule they wait in ambush and catch their prey in flight. Overview The Asilidae are a family in the order Diptera, the true flies. The common name for members of the family is the robber flies. The Asilidae are cosmopolitan, with over 7000 described species. Latreille was the authority for establishing the family in 1802.3 The Asilidae, together with Bombyliidae and Therevidae, are the most representative families of the superfamily of Asiloidea and they form one of the most characteristic groups of the lower Brachycera. Robber flies have stout, spiny legs and they have three simple eyes (ocelli) in a characteristic depression on the top of their head between their two large compound eyes.4 They also have a usually dense moustache of stiff bristles on the face; this is called the mystax, a term derived from the Greek mystakos meaning "moustache" or "upper lip". The mystax has been suggested to afford some protection for the head and face when the flies deal with struggling prey; various Asilidae prey on formidable species including stinging Hymenoptera, powerful grasshoppers, dragonflies and even other Asilidae, in fact practically anything of a suitable size. Some Asilidae do, however, specialize in smaller prey, and this is reflected in their more gracile build. In general the family attacks a very wide range of prey, including other flies, beetles, butterflies and moths, various bees, ants, dragon and damselflies, ichneumon wasps, grasshoppers, and some spiders. They do so apparently irrespective of any repugnatorial chemicals the prey may have at its disposal.5 Many Asilidae when attacked in turn do not hesitate to defend themselves with their proboscides and may deliver intensely painful bites if handled incautiously. The antennae are short, have three segments, and sometimes bear a bristle-like structure called an arista. Though they are a very characteristic group for such a large family, the Asilidae may easily be confused with the related and less widely-known family Therevidae. Some points of contrast between the families include that the labium in the Therevidae is not a piercing, predatory organ, but ends in two fleshy labella adapted to the sucking of liquid foods. Again, the Therevidae commonly have fluffy setae above the mouthparts, unlike the stiff chaetae comprising the mystax of the Asilidae. Furthermore, in the Asilidae the depression on the vertex between the eyes, tends to be more obvious than in the Therevidae. The fly attacks its prey by stabbing it with its short, strong proboscis injecting the victim with saliva containing neurotoxic and proteolytic enzymes which very rapidly paralyze the victim and soon digest the insides; the fly then sucks the liquefied material through the proboscis. Many Asilidae have long, tapering abdomens, sometimes with a sword-like ovipositor. Others, for instance Laphria are fat-bodied bumblebee mimics. The life histories are poorly known. Larvae generally seem to live in soil, rotting wood, leaf mold and similar materials, some being predatory and others detrivorous. Morphology Adults Adults are generally medium to large in size, with an average body length of 1 to 1.5 cm but with a range of 3 cm to more than 5 cm in length. The shape is generally elongated, due to the conformation of the long tapering abdomen, however there are also compact species with broad abdomens. The integument is covered with thick hair, especially on the head and thorax and liveries are often showy, with colors ranging from brown to black to grey, sometimes in contrast with other colors such as red and yellow. Frequently they are aposematic, imitating the livery of Hymenoptera. The head is free and mobile and dichoptic in both sexes and has three ocelli arranged in a characteristic depression formed by the elevation of the compound eyes. This feature is clearly visible in the front view and is a morphological peculiarity of Asilidae. The occipital region has one or more rows of bristles aligned behind the posterior margin of the eye. The facial region has a convex profile with a characteristic dense bundle of bristles, called a "mystax". The mystax helps protect the head and face when the fly encounters prey bent on defense. Other bristles are arranged on the ocellar tubercle. The antennae are of the aristate type, composed typically of 5 segments but sometimes from 3-4, depending on the structure of the stylus. The scape and pedicel are generally relatively short and hairy; the third segment (or first flagellomere) has an oval or oblong shape, is generally longer than the two basal segments, and bears a stylus generally composed of two segments, of which the basal is very short. In some asilids, the stylus can be monoarticolate or absent. The mouthparts are short and modified for piercing-sucking. They consist of a strongly sclerotized proboscis which includes the labium and maxillae which form a food canal, the labrum and a piercing organ, the hypopharynx. The proboscis is rounded in cross section or laterally or dorsoventrally compressed and is usually stout, and straight and sometimes able to penetrate through the hard integument of Coleoptera. The maxillary palpi are at the base beside the labium, two-segmented in all Dasypogoninae or single segmented in Asilinae and Leptogastrinae. The thorax is robust and compact. Unlike other lower Brachicera it bears long bristles (macrochaeta) useful as taxonomic characters. Bristles of this type are always present on the notopleuron (notopleural bristles) and, in two series, on mesonotum (dorsocentral, supralar and postalar). Other bristles are present on the metanotum (dorsocentral bristles on the ventral episternum and at the apex of the mesoscutellum. The legs are relatively long and strong, with many macrochaetes performing a repugnatorial function. The wings are well developed, often relatively narrow for speedy flight; the alula is generally well developed, with the exception of Leptogastrinae and part of Dasypogoninae. The venation is much as in Rhagionidae, Tabanidae and Therevidae; the radial R is always four-branched, with R2+3 unbranched. Details of wing venation determine subfamilies and lower taxa. The wings are most often hyaline, but sometimes smoky or dark colored, or partly infuscated in many genera or completely darkened. The abdomen consists of 6-8 visible segments preceding the genitalia in males, but the eighth segment is sometimes entirely or partially concealed, and terminal forming the ovipositor. It is long and narrow conical in most species but wide, dorsoventrally flattened and short in bee mimics. In Leptogastrinae the abdomen is extremely long and slender in Leptogastrinae. In some tribes, the male undergoes axial torsion of 180 degrees. Egg The egg is hyaline or pigmented and of variable shape from spherical to oval and up to 2 mm in length. The surface is smooth or bears microsculptures which are generally polygonal and visible only in the electron microscope. Larva The larva is apodous, cylindrical and elongated, more or less flattened dorso-ventrally and tapered at the cephalic and caudal ends. The colour is white or yellowish. The head is small, rugged, dark pigmented and hypognathous, the abdomen is composed of 8 apparent urites, with the last two often fused and more or less reduced. The respiratory system is of amphineustic, with two pairs of spiracles, one thoracic and one abdominal. There are also rudimentary and nonfunctional stigmas in other abdominal segments. Pupa The pupa is naked, as in the majority of Orthorrhapha, exarate and therefore able to move. Biology Category:Diptera